1. Field of the Invention
The present invention relates to an image forming apparatus that forms an image by the electrophotographic method such as a copying machine, a printer, a facsimile apparatus, and a multifunction peripheral.
2. Description of the Related Art
Conventionally, there has been an image forming apparatus that employs the electrophotographic method and operates according to a method employing an intermediate transfer belt as a transfer belt, as an image forming apparatus such as a copying machine and a printer. The image forming apparatus that operates according to the intermediate transfer belt method forms a full-color image by being subjected to a primary transfer process and a secondary transfer process.
During the primary transfer process, the image forming apparatus primarily transfers a toner image formed on a surface of an electrophotographic photosensitive member onto the intermediate transfer belt. The image forming apparatus forms toner images of a plurality of colors on a surface of the intermediate transfer belt by repeatedly performing the primary transfer process regarding the toner images of the plurality of colors. During the secondary transfer process, the image forming apparatus collectively transfers the toner images of the plurality of colors onto a surface of a transfer material such as paper. The toner images transferred onto the transfer material are fixed by a fixing device thereafter. As a result, a full-color image can be acquired.
A transfer device in the form of a roller, a transfer device in the form of a blade, a transfer device in the form of a brush, or the like is used as a transfer device of the image forming apparatus. These transfer devices are contact members that contact an inner circumferential surface (a back surface) of the intermediate transfer belt at a position facing the photosensitive member. Especially, the transfer device in the form of a brush includes a plurality of conductive fibers, and each one of the fibers can independently contact the back surface of the intermediate transfer belt. Therefore, the transfer device in the form of a brush can improve contact unevenness, which occurs when the transfer device in the form of a roller or the transfer device in the form of a blade is used. As a result, more even contactability can be obtained with the back surface of the intermediate transfer belt. This facilitates prevention or a reduction of an image defect such as density unevenness, which otherwise occurs during the primary transfer process.
Japanese Patent Application Laid-Open No. 2011-248385 discusses an image forming apparatus including a transfer device in the form of a brush. In the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2011-248385, a plurality of conductive fibers included in the brush is supported by a stainless-steel metallic holder via a double-faced adhesive tape. This metallic holder is fixed, and the plurality of conductive fibers included in the transfer member is in contact with a back surface of an intermediate transfer belt with the aid of elasticity of the fibers themselves.
However, the transfer device in the form of a brush is difficult to maintain excellent primary transferability, so that there has been a demand for development of various kinds of measures to improve it. The transfer device in the form of a brush can maintain each one of the fibers in perpendicular contact with the back surface of the intermediate transfer belt when the image forming apparatus is in an initial state. However, in a state after the image forming apparatus has been used, the fibers are tilted toward a downstream side in a movement direction of the intermediate transfer belt, whereby each one of the fibers is in contact with the back surface of the intermediate transfer belt in a bent state. At this time, a position of a contact region formed between the intermediate transfer belt and the fibers is displaced toward the downstream side in the movement direction of the intermediate transfer belt with respect to the position in the initial state. A large displacement of this contact region from the position facing the photosensitive member impairs the excellent primary transferability. Further, not only when the intermediate transfer belt is used as the transfer belt but also when a conveyance belt for conveying the transfer material is used as the transfer belt, this problem occurs in a similar manner.